Use of cation exchange chromatography for human C-peptide isotope dilution - mass spectrometric assay

An application of ion exchange chromatography for C-peptide analysis is described here. At the stage of C-peptide isolation, a strong cation exchanger (SP HP or MonoS) was used to purify the analyte from ballast proteins and peptides. The conditions of ion-exchange chromatographic separations were optimized using theoretical modeling of the net surface electric charge of the peptide as a function of pH. The purified and concentrated sample was further subjected to LC-MS/MS. In order to improve the reliability of analysis, two fragment ions were monitored simultaneously both for native C-peptide and internal standard, isotopically labeled C-peptides analogues (fragments with m/z of 927.7 and 147.2). Using ion-exchange chromatography, it became possible to process larger sample volumes, important for testing patients with very low C peptide levels, compared to currently used solid phase extraction methods.     

A complete 1H and 13C NMR data assignment for 3-phenylmethylene-1H,3H-naphtho-[1,8-c,d]-pyran-1-one

Complete assignments of the 1H and 13C NMR chemical shifts for 3-phenylmethylene-1H,3H-naphtho-[1,8-c,d]-pyran-1-one were done by means of one- and two-dimensional NMR techniques, including 1H-(1)H COSY, HMQC and HMBC spectra. Ab initio quantum chemistry calculations and a shift prediction by an incremental method provided values close to the proposed assignments. All mid-IR spectral bands are given as reference data. The DRIFT FTIR, ATR FTIR and Raman spectra are given as a Supplementary data in JCAMP-DX format, version 4.24. In addition, a method of compound's synthesis, that has the product yield higher as compared to already known data in the literature, is given.     

Polymer compatibility in two dimensions. Modeling of phase behavior of mixed polymethacrylate Langmuir films

We analyze the possibility of polymer blends undergoing phase separation in two dimensions. To this end, we investigate a model system consisting of water-supported Langmuir monolayers, obtained from binary polyalkyl-methacrylate mixtures (PXMA, where X stands for any of the type of ester side groups used: M, methyl-; E, ethyl-; B, butyl-; H, hexyl-; O, octyl-; L, lauryl-methacrylate), by means of self consistent field (SCF) calculations. In particular, we address the conditions which determine demixing and phase separation in the two-dimensional system, showing that a sufficient chain length mismatch in the ester side group moieties is able to drive the polymer demixing. When the difference in length of the alkyl chain of the ester moieties on the two types of polymers is progressively reduced, from 11 carbon atoms (PMMA/PLMA) to 4 carbons only (POMA/PLMA), the demixing tendency is also reduced. The polymer/subphase interactions affect more the distribution of the polymer coils in the POMA/PLMA blend monolayer. Mixing of the two polymers is observed, but also a partial layering along the vertical direction. We also add, to a PMMA/PLMA blended monolayer, a third component, namely, a symmetrical diblock copolymer of the type PLMA-b-PMMA. We observe adsorption of the diblock copolymer exclusively at the contact line between the two homopolymer domains, and a concomitant lowering of the line tension. The line tension varies with the chemical potential of the diblock copolymer according to Gibbs' law, which demonstrates that PLMA-b-PMMA can act as a "lineactant" (the equivalent of a surfactant in two-dimensional systems) in the binary demixed PMMA/PLMA Langmuir monolayer.     

Spectroscopic elucidation of the interaction of native cyclodextrins and their acetylated derivatives with asymmetric monomethyne cyanine dye

Five novel complexes of asymmetric monomethyne cyanine dye (1), with α-, β-, γ-cyclodextrins and the corresponding functionalized derivatives, namely acetyl-β-(Ac-β-CD) and acetyl-γ-(Ac-γ-CD) cyclodextrins were studied by means of UV–VIS, linear-polarized infrared and fluorescence spectroscopy, as well as scanning electron microscopy, powder X-ray diffraction, and thermal methods both in solution and in solid-state. Computational chemistry methods were employed with the purpose of elucidating the electronic structure and vibrational properties of the organic dye.     

The R3O+···H+ hydrogen bond: toward a tetracoordinate oxadionium(2+) ion

Oxatriquinanes are tricyclic oxonium ions which are known to possess remarkable solvolytic stability compared to simple alkyl oxonium salts. Their rigid, hemispherical structure presents an oxygen at the apex of three fused five-membered rings. While trivalent oxygen species like these have been well described in the literature, the ability of oxygen to enter into a fourth covalent bonding relationship has been visited in theory and suggested by the outcome of certain reactions conducted in superacidic media, but has never been established by the characterization of a stable, persistent R(3)OH(2+) or R(4)O(2+) ion. In this study, the nucleophilicity of the oxatriquinane oxygen was evaluated first by a series of protonation studies using the Br?nsted superacid H(CHB(11)Cl(11)) both in the solid state and in liquid HCl solution. The interaction of the oxatriquinane oxygen with a bridging carbocation was also examined. A strong case could be made for the occurrence of hydrogen bonding between H(CHB(11)Cl(11)) and oxatriquinane using IR spectroscopy. Under the most forcing protonation conditions, the oxatriquinane ring is cleaved to give a bridged, dicationic, protonated tetrahydrofuran-carbenium ion.     

Complexation of Carbamoylphosphine Oxide with Nitric and Perchloric Acids in Water-Dichloroethane Equilibrium Solutions

An IR spectroscopic study has established that in water-dichloroethane equilibrium solutions, carbamoylphosphine oxide forms only one complex with HNO₃, R'R₂P=O...HNO₃, whereas with HClO₄ it forms a number of solvation-separated ion pairs (IP). The structure and composition of the cation moiety of these IP depends on the molar ratio C_CMPO and the solution preparation temperature. A CMPO:HClO₄ = 2:1 complex is formed when C_CMPO/ > 2; for C_CMPO/C <2, 1:1 and 1:2 complexes and a complex with HClO₄ attached to the tertiary nitrogen of CMPO are formed. A detailed discussion is given for all complexes. It is shown for the first time that H⁺ can interact with three oxygen atoms of two P=O groups and one C=O group (or a water molecule) at once. In the absence of CMPO, dichloroethane extracts HNO₃ in the form of micelle-like associates, whose nucleus has a solubilized HNO₃ molecule in the form of a solvation-separated IP.     

2-Substituted imidazoles. 3. Metallation of 1-methyl-2-phenyl- and 1-methyl-2-(furyl-2)imidazoles

1-Methyl-2-phenylimidazole reacts with butyllithium to give 5-lithium substituted products. On the other hand, 1-methyl-2-(furyl-2)imidazole is metallated under the same conditions exclusively on the furan ring and primarily in the 3 position. The introduction of triethylamine into the reaction mixture, or replacement of butyllithium by lithium 2,2,6,6-tetramethylpiperidide leads to the formation of a lithium derivative substituted at the 5-position of the furan ring exclusively.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 61–66, January, 1992.     

IR spectroscopic investigation of the structure of polymeric uranyl di(2-ethylhexyl)phosphate molecules in C6H6 and CCl4 solutions

Using IR spectroscopy, we studied the types of coordination of POO groups in di(2-ethylthexyl)phosphate anionx X⁻ with UO ₂ ²⁺ cations in the C₆H₆ and CCl₄ solutions of the polymer molecules (UO₂X₂)_p. The polymers exhibit tridentate-bridge coordination (I), which is not typical of (MX_n)_p salts where the phosphoryl oxygen atom forms two bonds with U(VI) atoms. When a few U(VI) atoms (≳7%) interact with donar additives, all POO group I change their coordination to the usual bidentate-bridge type, , resulting in a structural transformation of the polymer. The bridging POO group are responsible for the difference in the dimerization and trimerization constants and the constants of the subsequent addition of the monomer molecules UO₂X₂ to the polymer chain (UO₂X₂)_p. It is suggested that type I coordination of X⁻ to U(VI) is due to an extended bond between the 2p²-electrons of the phosphoryl oxygen atom of the X⁻ anion and a vacant f-orbital of the U(VI) atom (p_π−f_π interaction). This unusual type of bond between uranium (VI) and tributyl phosphate (TBP) phosphoryl oxygen was found earlier for the UO₂Cl₂·2TBP complex. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturmoi Khimii, Vol. 35, No. 6, pp. 60–65, November–December, 1994. Translated by K. Shaposhnikova     

Charge separation and efficient light energy conversion in sensitized mesoscopic solar cells based on binary ionic liquids

A 7.4% power conversion efficiency at air mass (AM) 1.5 full sunlight was reached with a mesoscopic solar cell employing a new binary ionic liquid electrolyte composed of 1-propyl-3-methylimidazolium iodide and 1-ethyl-3-methylimidazolium tricyanomethanide in conjunction with the amphiphilic ruthenium complex NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-dinonyl-2,2'-bipyridine)(NCS)(2), coded as Z-907Na. Ultramicroelectrode voltammetric, nanosecond laser transient absorbance, and photovoltaic measurements show that a high iodide concentration is required for dye regeneration to compete efficiently with charge recombination. A surprisingly fast reductive quenching process is turned on in pure iodide melts. This channel is unproductive, explaining the lower photocurrents observed under these conditions.